Objectives: To purify and characterize a carcinogen-binding component that has been identified in the lung. Approach: The binding of 3-methylcholanthrene-H3 was examined in the cytosol from tissue of the rat. This revealed a binding component that is unique to the lung. To gain some insight as to the biological significance of this component, its physicochemical properties (size and composition) and its binding specificity are being analyzed.